1. Field of the Invention
This invention is generally directed to the delivery of fluids in medical procedures and, more particularly, to apparatus, systems, and methods of protecting pressure transducers used to obtain physiological pressure measurements during fluid delivery procedures.
2. Description of Related Art
In many medical diagnostic and therapeutic procedures, a medical practitioner such as a physician injects a patient with a fluid. In recent years, a number of injector-actuated syringes and powered injectors for pressurized injection of fluids, such as contrast media (often referred to simply as “contrast”), have been developed for use in procedures such as angiography, computed tomography, ultrasound, and NMR/MRI. In general, these powered injectors are designed to deliver a preset amount of contrast at a preset flow rate.
Angiography is used in the detection and treatment of abnormalities or restrictions in blood vessels. In an angiographic procedure, a radiographic image of a vascular structure is obtained through the use of a radiographic contrast which is injected through a catheter. The vascular structures in fluid connection with the vein or artery in which the contrast is injected are filled with contrast. X-rays passing through the region of interest are absorbed by the contrast, causing a radiographic outline or image of blood vessels containing the contrast. The resulting images can be displayed on, for example, a video monitor and recorded.
In a typical angiographic procedure, the medical practitioner places a cardiac catheter into a vein or artery. The catheter is connected to either a manual or to an automatic contrast injection mechanism. A typical manual contrast injection mechanism includes a syringe in fluid connection with a catheter connection. The fluid path also includes, for example, a source of contrast, a source of flushing fluid, typically saline, and a pressure transducer to measure patient blood pressure. In a typical system, the source of contrast is connected to the fluid path via a valve, for example, a three-way stopcock. The source of saline and the pressure transducer may also be connected to the fluid path via additional valves, again such as stopcocks. The operator of the manual contrast injection mechanism controls the syringe and each of the valves to draw saline or contrast into the syringe and to inject the contrast or saline into the patient through the catheter connection. The operator of the syringe may adjust the flow rate and volume of injection by altering the force applied to the plunger of the syringe. Thus, manual sources of fluid pressure and flow used in medical applications, such as syringes and manifolds, typically require operator effort that provides feedback of the fluid pressure/flow generated to the operator. The feedback is desirable, but the operator effort often leads to fatigue. Thus, fluid pressure and flow may vary depending on the operator's strength and technique.
Automatic contrast injection mechanisms typically include a syringe connected to a powered injector having, for example, a powered linear actuator. Typically, an operator enters settings into an electronic control system of the powered injector for a fixed volume of contrast and a fixed rate of injection. In many systems, there is no interactive control between the operator and the powered injector, except to start or stop the injection. A change in flow rate in such systems occurs by stopping the machine and resetting the injection parameters. Automation of angiographic procedures using powered injectors is discussed, for example, in U.S. Pat. Nos. 5,460,609; 5,573,515; and 5,800,397.
The pressure transducers used with automatic contrast injection mechanisms and manual contrast injection mechanisms used to conduct fluid injection procedures such as angiographic and like procedures are extremely sensitive to even moderate pressures generated during activation of the syringe, so the operator must typically close a valve to isolate the pressure transducer from the fluid path when the syringe is activated to prevent damage to the pressure transducer. Specifically, many pressure transducers can be damaged if they are subjected to pressures as low as about 75 psi. Because even a hand-held syringe can generate pressures of 200 psi or more, the isolation of the pressure transducer is essential in order to avoid pressure transducer failure. While the syringe is not activated, the valve is usually open to monitor patient blood pressure.
In one known arrangement, the pressure transducer and contrast injection mechanism are connected to the catheter through a manifold. The manifold includes a valve which enables the injector operator to isolate the pressure transducer during the injection of the contrast solution. This valve, typically a stopcock, is used to isolate the pressure transducer to prevent damage thereto. Specifically, a stopcock configuration is provided which either allows the pressure transducer to be in fluid communication with the catheter or the contrast injection mechanism to be in fluid communication with the catheter, but not both. Typically, the stopcock handle must be turned manually to switch between the two positions. Accordingly, this configuration provided by some currently available manifolds does not allow contrast injection to be made while the pressure transducer is in communication with the catheter.
One problem associated with the foregoing valve-manifold design is that the operator often forgets to turn the stopcock back to the position where the pressure transducer is in fluid communication with the catheter. As a result, the monitoring of the vessel or artery is interrupted for time periods longer than necessary. The monitoring of the vessel or artery pressure is important during almost any vascular procedure. Accordingly, when the operator fails to turn the stopcock handle, other members of the medical team must interrupt the operator and tell him or her to turn the pressure transducer back on which may cause an unnecessary distraction during a delicate medical procedure.
A well-established pressure transducer protection design includes, typically, a two-pieced housing formed from generally hemispherical members that form a “pressure dome” wherein a generally planar diaphragm or membrane is positioned. The diaphragm or membrane is centered within the housing and has a thickness that permits deflection within the housing in response to a pressure differential within the pressure dome. Thus, the diaphragm or membrane deflects or stretches in response to a pressure differential and this deflection is transmitted via a suitable pressure transmitting media in the pressure dome to the isolated pressure transducer. Examples of the foregoing diaphragm-type pressure transducer isolator design are disclosed in U.S. Pat. No. 4,314,480 to Becker; U.S. Pat. No. 4,226,124 to Kersten; U.S. Pat. No. 4,077,882 to Gangemi; and U.S. Pat. No. 3,863,504 to Borsanyi; U.S. Pat. No. 3,713,341 to Madsen et al.; and U.S. Pat. No. 3,645,139 to Zavoda, as examples. In the non-medical area, examples of pressure isolation devices for pressure gauges are disclosed in U.S. Pat. No. 3,207,179 to Klagues and U.S. Pat. No. 2,191,990 to Jordan.
U.S. Pat. No. 6,896,002 to Hart et al. discloses a pressure transducer protection device particularly adapted for angiographic fluid delivery systems. The pressure transducer protection device disclosed by this patent is in the form of a pressure activated valve for a three-way connection between a catheter, an injector, and a pressure transducer. The valve includes a body that has an inlet for connection to an injector, an outlet for connection to a catheter, and a secondary connection for connection to a pressure transducer. The body also includes a seal seat disposed between the secondary connection in both the inlet and the outlet. The body is flexibly connected to a plug seal. The plug seal is disposed between the seal seat in both the inlet and the outlet. The plug seal is movable between an open position spaced apart from the seal seat and biased towards the inlet and the outlet and a closed position against the seal seat thereby isolating the secondary connection from both the inlet and the outlet.
Another valve used for pressure transducer protection purposes is disclosed by U.S. Patent Application Publication No. 2006/0180202 to Wilson et al. This publication discloses an elastomeric valve having a valve body with three ports including a contrast inlet port, a saline inlet and pressure transducer port, and a patient or outlet port. The valve body houses a disc holder and a valve disc therein. The valve disc is molded of an elastomer, such as silicone rubber, with a slit in the center. The elastomeric disc is sandwiched between the valve body and disc holder and is affixed therebetween at the perimeter of the disc. Such affixation may be effected by entrapment, adhesion, mechanical or chemical welding. The elastomeric valve disclosed by this publication is responsive to pressure changes in the valve which act on the elastomeric disc.
Despite the contributions of Hart and Wilson et al., there is a general need for an improved pressure transducer protection device which can operate automatically to isolate a pressure transducer used to obtain physiological pressure measurements, particularly those pressure transducers used in potentially damaging fluid pressure environments such as angiography.